Reusable storage containers have been in use for many years and enable consumers to store leftovers and other food products. One problem associated with such storage containers is that it is difficult to keep track of the date when the food was stored in the container. Similarly, it is difficult to keep track of the date by which the food should be disposed.
Since most currently available food storage containers do not include any indicator to enable the user to mark the date when the food was placed in the container, quite often these containers are placed into the refrigerator or freezer without any date indication at all. This poses a serious health concern to the consuming public, as the FDA has shown that millions of Americans are stricken by illness every year caused by the food they consume and that approximately nine-thousand (9,000) people a year die of food poisoning By simply storing food in the food storage container without indicating the date on which the food was placed in the container, there is a possibility that the food in the container will go rancid prior to being consumed In the event that the food is not spoiled to the point that it is visibly noticeable to the consumer, there is a possibility that the consumer will eat the spoiled food and become sick and/or die of food poisoning. Consequently, there is a need for a device that will give consumers confidence when judging the freshness of foods stored in the refrigerator and freezer. Such a device would also eliminate a common situation that creates—guilt contemplating the disposal of food of uncertain age.
In an attempt to indicate the date upon which the food in a container was stored various companies offer “freezer tape,” which is essentially tape upon which notes and other indicia can be written. This tape is placed on the lid of the food storage container and a storage date is written on the tape. However, this method is quite inconvenient, as the use of this product requires the consumer to apply the tape to the container (removing any old tape which remains from any previously stored food) and write the food storage date on the freezer tape itself. Further, this tape will only stick to a container that is dry and not very cold. Additionally, this handwritten date is often blurred and unreadable once exposed to frost or cold moist air. All these inconveniences add up to a system that is overly burdensome to use. As a result, such a system is unlikely to be used.
There have been other attempts to design an effective system for dating the contents of food and other containers. For example, Owens (U.S. Pat. No. 4,985,879), describes a container which indicates the date using arms reminiscent of a clock. Hornung (U.S. Pat. No. 6,000,159) describes a date using a device reminiscent of a car odometer. Designs such as those of Owens and Hornung are problematic in that the lid and date apparatus must be assembled from a number of different parts. Such assembly can significantly increase the cost of production. Such assemblies are also particularly ill-suited for a reusable container, because the parts can break or fall apart after repeated use of the container. What is needed is a simpler date indicating design that is easier to assemble, less expensive to produce, and less likely to become damaged.
The past is replete with the use of dimples or deformable surfaces for indicating the contents of disposable, fast food beverage lids. Examples include Wolf (U.S. Pat. No. 3,392,468) and Bartolucci (U.S. Patent No. 3,974,916). However, such dimples or buttons have not been used to indicate the date of a reusable container's contents. Moreover, such a use is by no means obvious. First, the beverage lids are disposable with the contents meant for immediate consumption, so there would be no need to indicate a date. Second, and more importantly, one of ordinary skill would not anticipate success in applying the art of disposable beverage lids to reusable containers and lids.
One would not anticipate success in applying the art of disposable beverage cups to reusable containers and lids on account of a great number of different factors. Some important factors are duration and repetition of use, number of buttons, the container's dimensions and material composition, and, finally, environmental stresses. These factors are all related and collectively influence the stability of date-indicating buttons. The first of these four factors is the most straightforward. A reusable container has to be very sturdy to stand up to repeated uses, and that is true even independent of such factors as material composition and environmental considerations, which are discussed below. The buttons on disposable beverage lids are generally for the immediate use of restaurants, which often have to dispense a lot of different beverages simultaneously to many different patrons. The buttons exist principally for the aid of the restaurant, and not the consumer. Consequently, the buttons on such disposable lids only need to remain stably inverted for a very brief period of time. And even if a single consumer has bought several different beverages, and so needs to tell them apart, such beverages will be consumed or dispensed to others in a very brief period of time.
The standard disposable beverage lid contains only four buttons, see, e.g., the Wolf and Bartolucci patents. Four buttons is usually not sufficient for indicating a date on a reusable food storage container. Simply adding more buttons for use in a reusable storage container using existing button designs is not feasible. Since the buttons are part of a common piece of plastic, the forces on one button are going to be shared to at least some extent by the other buttons. When there are many buttons on a single container or lid, the stresses can be enough to compromise button stability.
The plastics used in disposable beverage lids are generally different from those used in reusable containers and lids. The most common design found on thin thermoformed polystyrene beverage lids consists of a simple dome. Unfortunately, when such buttons are formed in the thicker polypropylene lids typically used for home (reusable) food storage containers, this design yields completely unsatisfactory results. Due to the higher overall stiffness and resilience of lids on home food storage containers, a button having a geometry akin to those on a disposable beverage lid will quickly and automatically pop back up to its original conformation.
Stiffness is one part of the problem because a stiffer material poses a greater resistance to inversion. Polystyrene (PS) has a higher intrinsic stiffness (elastic modulus) than polypropylene (PP), polyethylene (PE), or polypropylene/polyethylene (PEP) copolymers, for example. Unfortunately, the thicker lid stock typically employed with the latter materials more than offsets the intrinsic advantage in flexibility since extrinsic stiffness (moment of inertia) increases in proportion to the cube of the thickness. Thermal sensitivity is another problem. The softening points of low density PE (LDPE), PS and polythethylene terepthalate (PET) are low for parts used in a microwave for example. PP and HDPE hold up better in the microwave but are generally stiffer than a PEP. Reducing flexural rigidity solely through a reselection of raw materials is therefore not a satisfactory solution. Nor is a reduction in thickness, because a certain amount of rigidity is necessary to connote a sense of lid security and to form satisfactory seals in the eyes of consumers.
Fina 6289MZ PP, being a random ethylene/propylene copolymer is one of the more flexible choices for a lid's raw material that does not excessively compromise thermal properties. Unfortunately, the exceptional resilience of PEP, a common plastic used in reusable containers, is another problem for attempting to translate beverage lid buttons to reusable storage containers and lids. A resilient material has a high level of elastic memory of its former conformation. Displacement of a button surface from its original position creates stresses which then act toward reverting the button after external forces are removed. In a brittle material like PS, which has a glass transition temperature above room temperature, the stresses experienced during a button inversion cause the material to fail on a microscopic scale. Very small fissures (crazing or stress-whitening) form in the surface. This relieves much of the stress, greatly reducing the restorative forces available for a reversion. A brittle material, while beneficial from this vantage point, would be unsuitable for a storage container used inside a freezer. A moderate impact would cause a cold container to shatter. Even more significant, crazing is an irreversible process, which can make PS unsuitable for use in a reusable container. While crazing may also affect buttons composed of other plastics, including PEP, the visual effects are reversible, and the physical effects are less severe.
A reusable storage container and lid, must withstand the heat of a microwave, the cold of a freezer/refrigerator, and the abuse of a dishwasher. The container must also have a balanced stiffness so that it may produce a good container seal and still permit inversion of buttons without too much difficulty. These requirements preclude simply selecting a particular type of plastic that would make pre-existing button designs functional on a reusable storage container. Since applying existing button designs to reusable containers and lids does not work, there is a pressing need for button designs that will be effective for use in reusable lids and containers.